The invention relates generally to a communication system comprising at least two communication terminals electromagnetically coupled to each other through a transponder and more particularly to communication terminals forming a closed loop oscillation for focusing the antenna arrays of the respective communication terminals.
Generally, it is known that two communication terminals each having an antenna array can be used to obtain a retrodirective oscillating loop for focusing the respective antenna arrays even for noise signals. In this connection, reference is had to applicant's U.S. Pat. No. 3,757,335 and his co-authored article "Self-Directional Microwave Communication System," IBM Journal of Research and Development, March 1974, pages 149 to 163.
Generally, a retrodirective oscillating loop between two communication terminals features the transfer of electromagnetic energy from communication terminal through space to the other communication terminal where the electromagnetic signal is amplified and retransmitted back to the first communication terminal where it is again amplified and retransmitted and this process continues indefinitely. If the total loop gain is greater than the total loop loss, there will be a build-up of signal even without the initial transmission of a carrier.
The build-up of signal or oscillation between the two retrodirective communication terminals may be seen from the following.